Packaging containers of the single use disposable type for liquid foods are often produced from a packaging laminate based on paperboard or carton. One such commonly occurring packaging container is marketed under the trademark Tetra Brik Aseptic® and is principally employed for aseptic packaging of liquid foods such as milk, fruit juices etc, sold for long term ambient storage. The packaging material in this known packaging container is typically a laminate comprising a bulk core layer of paper or paperboard and outer, liquid-tight layers of thermoplastics. In order to render the packaging container gas-tight, in particular oxygen gas-tight, for example for the purpose of aseptic packaging and packaging of milk or fruit juice, the laminate in these packaging containers normally comprises at least one additional layer, most commonly an aluminium foil.
On the inside of the laminate, i.e. the side intended to face the filled food contents of a container produced from the laminate, there is an innermost layer, applied onto the aluminium foil, which innermost, inside layer may be composed of one or several part layers, comprising heat sealable thermoplastic polymers, such as adhesive polymers and/or polyolefins. Also on the outside of the core layer, there is an outermost heat sealable polymer layer.
The packaging containers are generally produced by means of modern, high-speed packaging machines of the type that form, fill and seal packages from a web or from prefabricated blanks of packaging material. Packaging containers may thus be produced by reforming a web of the laminated packaging material into a tube by both of the longitudinal edges of the web being united to each other in an overlap joint by welding together the inner- and outermost heat sealable thermoplastic polymer layers. The tube is filled with the intended liquid food product and is thereafter divided into individual packages by repeated transversal seals of the tube at a predetermined distance from each other below the level of the contents in the tube. The packages are separated from the tube by incisions along the transversal seals and are given the desired geometric configuration, normally parallelepipedic, by fold formation along prepared crease lines in the packaging material.
The main advantage of this continuous tube-forming, filling and sealing packaging method concept is that the web may be sterilised continuously just before tube-forming, thus providing for the possibility of an aseptic packaging method, i.e. a method wherein the liquid content to be filled as well as the packaging material itself are reduced from bacteria and the filled packaging container is produced under clean conditions such that the filled package may be stored for a long time even at ambient temperature, without the risk of growth of micro-organisms in the filled product. Another important advantage of the Tetra Brik®-type packaging method is, as stated above, the possibility of continuous high-speed packaging, which has considerable impact on cost efficiency.
Packaging containers for sensitive liquid food, for example milk or juice, can also be produced from sheet-like blanks or prefabricated blanks of the laminated packaging material of the invention. From a tubular blank of the packaging laminate that is folded flat, packages are produced by first of all building the blank up to form an open tubular container capsule, of which one open end is closed off by means of folding and heat-sealing of integral end panels. The thus closed container capsule is filled with the food product in question, e.g. juice, through its open end, which is thereafter closed off by means of further folding and heat-sealing of corresponding integral end panels. An example of a packaging container produced from sheet-like and tubular blanks is the conventional so-called gable-top package. There are also packages of this type which have a moulded top and/or screw cap made of plastic.
A layer of an aluminium foil in the packaging laminate provides gas barrier properties quite superior to most polymeric gas barrier materials. The conventional aluminium-foil based packaging laminate for liquid food aseptic packaging is still the most cost-efficient packaging material, at its level of performance, available on the market today.
Any other material to compete must be cost-efficient regarding raw materials, have comparable food preserving properties and have a comparably low complexity in the converting into a finished packaging laminate.
Among the efforts of developing non-aluminium-foil materials for liquid food carton packaging, there has been a general incentive towards developing pre-manufactured films or sheets having high barrier properties, i.e. not only oxygen and gas barrier but also water vapour, chemical or aroma-substance barrier properties, from expensive materials and material combinations, however often not sustainable from an environmental and sourcing point of view.
An important driving force behind developing non-aluminium-foil based barrier packaging materials, is to use renewable raw materials as far as possible, in order to lower the total emitted CO2 content connected to the materials used and to the manufacturing process of the packaging material.
A very interesting such alternative non-foil, as well as renewable, barrier material would be so called cellulose nanofibrils, CNF, also commonly named as micro- or nanofibrillar cellulose (MFC, NFC).
CNF is normally produced by a method having a first pre-treatment step to treat cellulose pulp by chemicals, such as enzymes or, alternatively by oxidation, and a second step involving mechanical disintegration of the cellulose fibres into nano-thin fibrils.
A further important and relevant advantage of CNF as a barrier material, is the fact that it would be recyclable together with the conventional cellulose material present in any paper or carton packaging, and thus will not need to be separated from the paper stock or paper layers of a laminated packaging material.
CNF has the disadvantage of being very moisture-sensitive, losing its gas barrier properties as it absorbs moisture in a packaging material. In particular for the purpose of liquid or semi-solid packaging, this is a draw-back of CNF materials.